Some data on the spontaneous fission of Cm244

The average kinetic energy of the fission fragments, , the distribution width at half the height, E_k = 24.8 ± 2.5 MeV, and the average number of prompt neutrons per fission, = 2.71 ± 0.04, are found for the spontaneous fission of Cm²⁴⁴. The variation of and as functions of the nucleonic composition of the fissionable nucleus is considered in connection with the experimental results. Attention is drawn to the correlation of anomalies in these functional relationships as the most probable fragment mass varies. The assumption that the observed effects are related to a variation in the elastic properties of the fragments produced is discussed.Translated from Atomnaya Énergiya, Vol. 17, No. 1, pp. 28–34, July, 1964     

Nuclear information obtainable from low energy neutron spectroscopy

The results of measurements of thermal-neutron cross sections, level distributions in the resonance region, ratios, and determinations of the effective nuclear radius from potential:.scattering of slow neutrons are considered.A discrepancy in the results of measurements of the thermal-neutron fission cross secticn in U²³⁵ is noted. The distribution of levels exhibits a deficiency in small spacings as compared with a random distribution, i. e., there seems to be a repulsion of levels. The dependence of on atomic number A is nonmonotonic, in accordance with the complex-potential model of the nucleus; however there is a considerable discrepancy between the experimental data and theory for atomic numbers in the neighborhood of 100. The effective radius determined from potential scattering of slow neutrons indicates a nonmonotonic dependence on A, in agreement with the model of a semi-transparent nucleus with smeared-out edges.     

Analysis of the observed resonance-width distributions of U233 and Pu239

As a result of the strong fluctuations of fission and reduced neutron widths, a significant number of resonances occur with such a small reduced height 2gF_n ⁰/ that they will not be noticed experimentally. If the fraction of transmitted resonances is considerable, then this should lead to the following effects which might be observable in an experiment: 1) change of the distribution function of the reduced neutron and fission widths, which is particularly sharply manifested for _n ⁰/<_n ⁰> 1 and _f/<_f> 1; 2)appearance of correlation between the form of the neutron distribution b of fission channels; 3) appearance in the total cross section and fission cross section of a background which is approximately proportional to . All the effects mentioned are manifested for the U²³³ nucleus. For Pu²³⁹ this effect is smal! and the observed values are welI described by X² distributions.Translated from Atomnaya Énergiya, Vol. 17, No. 1, pp. 22–27, July, 1964     

Dosimetry method for β radiation based on investigations of the electron spectra in the fields of β emitters

A method has been developed for -ray dosimetry based on the investigation of the effective electron spectra in the fields of emitters. The spectra was investigated with the help of a scintillation spectrometer. It was shown, that the value of the dose , where N is the number of particles penetrating an infinitesimal volume around the point being considered; is the value of the ionization loss averaged over the spectrum. It was established that the quantity is determined by the maximum energy of the spectrum of the isotope and may be considered to be independent of the depth of the medium and of the source diameter. Curves of depth doses for S³⁵, Tl²⁰⁴, Y⁹¹, and Ce¹⁴⁴ + Pr¹⁴⁴ are given and criteria for selecting isotopes to provide optimal conditions of irradiation are established.     

Distribution of the ratio of radiation capture and fission cross sections for Pu239 with respect to height in the BR-5 reactor

A study was made of the distribution of the ratio of radiation capture and fission cross sections for Pu²³⁹ with respect to height in the BR-5 reactor. The distribution of neutron capture reactions was measured by determining the concentration of Pu²⁴⁰ from the rate of spontaneous fissions in plutonium samples irradiated in the reactor with an integral flux of 10²¹ to 10²² neutrons/cm². As initial material for irradiation, almost isotopically pure Pu²³⁹ (Pu²⁴⁰ content 5·10^–3% was used. The values of obtained rose from 0.1 to 0.8 on moving away from the center of the reactor. The data corresponding to equilibrium neutron spectra in the active zone and the outer region of the reflector agree with the results of measuring and _f in monoenergetic neutrons.Translated from Atomnaya Énergiya, Vol. 16, No. 6, pp. 497–500, June, 1964     

Effective cross sections for fission of U233, U235, Pu239 and Pu240 by neutrons with energies from 30 kev to 5 Mev

Measurements have been made of the absolute values of the effective fission cross sections in U²³³, U²³⁵, Pu²³⁹ and Pu²⁴⁰, using as photoneutron sources Sb + Be ( 30 kev), Na + D₂O ( 250 kev), Na + Be ( 900 kev), a source with a simulated fission-neutron spectrum and Po--Be. The fission cross sections for 30 kev-neutrons are 3.06 ± 0.16, 2.21 ± 0.12 and 1.79 ± 0.11 barns for U²³³, U²³⁵ and Pu²³⁹, respectively. As the neutron energy Is increased from 30 kev to 250 kev the cross sections in U²³³ and U²³⁵ fall off by approximately 35% and then remain almost constant while the cross section in Pu²³⁹ falls off by 12% and then increases. The effective cross sections for fission in Pu²⁴⁰ for 900-kev and 5-Mev neutrons is 1.4 barns and the threshold for fission in Pu²⁴⁰ lies within the limits 250 and 900 kev.In conclusion the authors wish to express their gratitude to P. E. Spivak for help in formulating the problem and a discussion of the results.     

Direct measurement of the energy variation of η for U233, U235, and Pu239

A technique is described that measures directly the energy variation of , the number of fission neutrons produced per neutron absorbed. When combined with total cross sections, the method is capable of giving fission cross sections as well. Results are presented in the energy region near thermal, of importance to reactor design, for U²³³, U²³⁵, and Pu²³⁹. Comparison with computed from total and fission cross sections shows good agreement for U²³³ and U²³⁵ but a disagreement outside experimental error for Pu²³⁹. An auxiliary experiment demonstrates that , the number of neutrons per fission, is constant with energy in the region of interest for Pu²³⁹, hence that the discrepancy cannot be ascribed to a variation.Work performed under contract with U. S. Atomic Energy Commission.[The following is a reproduction of the original American paper, and not a re-translation from Russian — Publisher's note].     

Relative measurements of the mean number of neutrons emitted in fission of U233, U235 and Pu239 by thermal neutrons and by neutrons characteristic of a fission spectra

The ratios of the mean number of neutrons () emitted in the fission of U²³³, U²³⁵ and Pu²³⁹ by thermal neutrons and by neutrons characteristic of a fission spectra have been measured. A method was employed in which the number of fission events was counted simultaneously with the number of coincidences between fragments and fission neutrons. It is found that the quantity increases by approximately 10% in all isotopes which were investigated.In conclusion the authors wish to thank P. E. Nemirovsky for the interest which he has taken in this work.     

The distribution of ionization along a beam of γ-radiation and the determination of radiation dose with normal ionization chambers

It was established that the ionization effect, measured in normal ionization chambers for determining the dose in a region of -radiation, must be referred to a point in space, displaced by a distance of about from the center of the measuring electrode of the chamber towards the source. The corrections for displacement of the measuring volume for the -radiation of Cs¹³⁷ and Co⁶⁰, respectively, equal 0.996 and 0.992.     

Some characteristics of a fast reactor with thorium shield

The regeneration factor of Pu²³⁹ in U²³³ was determined in the BR-1 experimentaI fast reactor with a Pu²³⁹ core and a Th²³² shield. The breeding characteristics of thorium, the utilization factor of fission neutrons (D) and the neutron multiplication factor (k) were also studied.Translated from Atomnaya Énergiya, Vol. 17, No. 4, pp. 294–299, October, 1964Deceased     

Calculating the transient temperature field in a reactor tube and the thermoelastic stresses in the fuel element cladding

Approximate analytic methods are given for calculating the transient temperature field in the fuel elements and the coolant temperatures at any point along the reactor tube, as well as the transient thermoelastic stresses in the cladding of a cylindrical fuel element. The coolant temperature at the input to the tube is constant, and the coolant undergoes no changes in state of aggregation. The approximate methods are illustrated by examples.Results are given, for comparison, of accurate calculations of the same examples made with a rapid calculating machine.List of symbols time - r; z coordinates (radius, distance along tube) - r₁; r₂ internal and external radii of fuel element cladding respectively - H total active length of fuel element - a₁; ₁;c _{1 1} coefficients of temperature conductivity, heat conductivity, specific heat capacity and specific gravity of fissionable material respectively - a₂; ₂; C_p2; ₂ cladding parameters - a; ; c_p; coolant parameters - mean cladding radius - f:f₂ cross-sectional area of tube for coolant and cladding respectively - w coolant velocity - coefficient of heat release to coolant - t (r, ); (); () fuel temperature, mean temperature over cross section of cladding, and coolant temperature at pointz. along tube respectively - qv() specific volume of coolant at pointz - values averaged overz - quantities at the initial instant of time - ₃ delay time - _n time required for coolant to go from z=0 to the point in question     

Deformation systems of α-zirconium

The deformation systems of -zirconium iodide have been studied in coarse-grained polycrystalline specimens deformed by upsetting. The orientation of the grains was determined from Laue patterns obtained in a special back-reflection camera using a small-diameter beam. The indices of the deformation systems were determined by the two-surface method and by the pole locus method.It was found that -zirconium is deformed by slip along the plane in the direction and along the plane. A number of twinning systems have been discovered In -zirconium: a) K₁ , 1 , K₁ , ₂ and s=0.173; b) K₁ , ₂ [1126], K₂ (0001), ₂ [1120] and s=0.629; c) K₁ (1122), ₁ [1123] and in one case, d) K₁ , ₁ .     

Average energies of electron and positron β spectra

The average energies of electron and positron spectra were calculated for various values of the atomic number Z of radioactive nuclei and the timiting energy E₀ of the spectrum. The calculations were carried out for the case of allowed transitions and unique transitions of the first order of forbiddenness. The report contains tables and graphs of the values of and = f(E₀, Z) which may be used in evaluating the thermal effects of various radioactive specimens, nuclear reaction products, and products resulting from the fission of dements under the action of slow neutrons and high-energy nucleons, in calorimetric measurements of radioactive sources, and in calculating certain dosimetric characteristics of specimens which emit radiation. The authors give a brief survey of the methods of determining the average energies of spectra and the values of these quantities obtained up to the present time for various radioactive isotopes.Translated from Atomnaya Énergiya, Vol. 17, No. 1, pp. 9–17, July, 1964     

Analytic representation of the fission neutron spectra of235U and252Cf

Analytic representations of the spectra in two forms—in the form of a model spectrum and as a sum of nine model spectra , where α_i=4.2.1.333.1.0.0.8.0.4.0.2.0.05. and 0.01-are obtained on the basis of representative sets of integral cross sections for the fission neutron spectra of²³⁵U due to thermal neutrons and spontaneous fission spectra of²⁵²Cf.2 tables. 5 references. Translated from Atomnaya énergiya, Vol. 88, No. 4, pp. 299–303, April, 2000.     

Distribution of fragments by mass in fission of U235. U238 and Pu239 by neutrons of 14.6 Mev energy

A study of the mass distribution of fission fragments provides a better understanding of the fission process for heavy nuclei. In addition, a knowledge of the relative yield of various fragments is necessary in some practical uses of radioactive isotopes.In this paper the method and results of measurements of the relative production of several fragments, formed in the fission of U²³⁵, U²³⁸ and Pu²³⁹ by neutrons with energy of 14.6 Mev, are given. By experimental and reflected points, curves are obtained for the distribution of fragments by masses. Some special features of this distribution are interpreted.     

Measurement of η and partial cross sections of nuclides U235 and Pu239 for resonance neutrons

Values of and total neutron cross sections of the nuclides U²³⁶ and Pu²³⁹ were measured on a neutron spectrometer, using a pulsed cyclotron beam [1]. Energy relations of the cross sections for fission and radiative capture in the neutron energy region from thermal energies up to 20 eV for U²³⁵ and from 5 to 100 eV for Pu²³⁹ were obtained, The parameters of an appreciable number of resonances were determined.Translated from Atomnaya Énergiya, Vol. 16, No. 2, pp. 110–119, February, 1964     

Determination of the intensities of neutron sources from the activity induced by the neutrons in a solution of potassium permanganate

The intensity of a Ra-Be neutron source is measured by means of the activity induced by the neutrons in an aqueous solution of potassium permanganate. The major part of the activity Mn⁵⁶ produced by the capture of neutrons slowed down in the water was separated in the form of manganese dioxide fay ordinary filtering. To take account of the neutrons captured by the hydrogen, the ratio of the effective cross sections for capture of thermal neutrons by manganese and by hydrogen was measured and found to be . It was found that the intensity of the two sources studied amounts to 10,600 ± 500 neutrons/sec per milligram of radium.Work carried out in 1051. Printed in reports of the Academy of Sciences of the USSR in 1951 and 1952.     

Scattering of medium-energy neutrons

Conclusion A study of inelastic-scattering processes as a function of neutron energy and the number of nucleons in the nucleus has enabled us to observe and investigate the effects of the nuclear shells in inelastic scattering. Experimental data on the inelastic-scattering cross sections have been used to check the optical model of the nucleus with a diffuse edge [23].The values of nuclear-physical constants (_e,_tre, ) obtained from the measured angular distributions of elastically-scattered neutrons may be used for calculating multigroup constants [24] required for physical calculations of nuclear-power systems and biological protection (shielding). The experimental material on the angular distributions of elastically-scattered neutrons has enabled us to verify the applicability of the optical model for describing elastic-scattering processes at energies below 1 MeV.Part of the information obtained on the elastic- and inelastic-scattering cross sections and the angular distributions of elastically-scattered neutrons has been included in handbooks on nuclear-physics constants [25–27].Translated from Atomnaya Énergiya, Vol. 20, No. 1, pp. 8–17, January, 1966     

Simulation of nuclear-fuel solvent-extraction reprocessing 7. Separation of macroscopic amounts of plutonium and uranium by displacement reextraction of plutonium in reprocessing fast-reactor fuel (section 1)

Conclusions These data have been obtained from simulating displacement reextraction in a system with two inputs (system for reprocessing a fast-reactor fuel), and they show that it is possible to obtain a uranium extract with not more than 100 g Pu/kg U in a counter current system with 18 stages to provide partial separation of the uranium and plutonium by reprocessing of an organic solution containing U⁺ Pu (10 1) with 64% saturation in the sum of the metals to produce reextract containing plutonium with U : Pu3 and over 99.99% extraction of the uranium; this requires 90 g/liter of uranium in the reextractant and the parameters n=2.06–2.00 ( =0.3 M); n=1.82–1.87 ( =0.5 M); n=1.61–1.78 ( =1.0 M).Full data obtained from the simulation are to be found in [5], from which one can extract the parameters of the working state of the extractor and other data on the separation of uranium and plutonium, e.g., for other specifications for the plutonium level in the uranium. The next part of the present study will be concerned with engineering solutions that can extend the range of conditions that provide the appropriate output parameters within specified ranges and thereby improve the reliability in operating the process in the optimal region.Translated from Atomnaya Énergiya, Vol. 47, No. 6, pp. 377–381, December, 1979.     

Chemical potential of oxygen of UO2 close to stoichiometry

Conclusions A closed solid electrolyte cell, permitting reliable values of to be obtained up to –775 kJ/mole, using a ceramic oxygen pump of stabilized ZrO₂, was developed. The temperature dependence of of uranium dioxide was determined for O/U=2.0039; 2.0021; 2.0018; 2.0012; 2.0009, and 2.0006. Coulometric titration of uranium dioxide was performed in the range of O/U from 2.0039 to 1.9991, and the influence of the degree of nonstoichiometry on was studied at 1273°K. A very strong dependence of at 1273°K was demonstrated in the range of O/U from 2.0001 to 1.9999. A change in O/U by 0.01% causes a 70% decrease in .Translated from Atomnaya Énergiya, Vol. 51, No. 4, pp. 228–230, October, 1981.